The first part of this paper describes a computer program which uses equations derived by the Rayleigh-Ritz technique to model the vibrations of rectangular orthotropic plates. The characteristic functions of vibrating beams were used as the assumed functions for plates with boundary conditions consisting of clamped and free edges. Resonant frequencies and mode shapes from the program were verified by finite element analysis and modal analysis for square aluminum and graphite/epoxy plates. The plate vibration model was then incorporated into a second computer program which was designed to use the measured resonant frequencies of orthotropic plates to determine the four apparent elastic constants. Resonant frequencies measured by an impulse technique were used to determine two Young's moduli, the in-plane shear modulus, and a Poisson's ratio for each plate.
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